1. Field of the Invention
The present invention relates to digital systems, and is more particularly concerned with determining on which of two given wave forms a transition first occurs.
2. Description of the Prior Art
In working with digital systems, it is often necessary to know the relationship between transitions in wave forms. More particularly, it is often necessary to determine which of two wave forms first undergoes a transition from a first state to a second state.
One area where the time relationship between wave form transitions is of value is in measuring the signal propagation time through a system. In such an arrangement, it is often desirable to have a simple means for monitoring the time relationship between transitions and thereby know which wave form first undergoes a transition.
In the past, such objects were achieved in various ways. One way was to have a clock source and a counter, with gating means so that the occurrence of a transition on one wave form would initiate the counter counting clock pulses, and the occurrence of the transition on the second wave form would halt the counting process. The value in the counter would then be indicative of the time relationship between the transition of the two wave forms.
An alternate method of ascertaining the time between transitions in two wave forms was to use either a dual trace oscilloscope, or a single trace oscilloscope with a means of triggering the trace from an external source, which in this application would be one of the two wave forms. The time relationship between the two wave forms could then be directly observed on the oscilloscope screen.
However, both of the above-described methods, as well as the many other techniques, often suffer from the requirement of various amounts of highly complex and expensive equipment. In addition to this, when the time between the transitions becomes very small, typically in the sub-nanosecond range, the speed at which the equipment can operate can begin to limit the effectiveness of the observance and measurability of the events.